Power semiconductor devices, such as, for example, radio frequency (RF) power amplifiers fabricated using a laterally diffused metal-oxide-semiconductor (LDMOS) process technology, often comprise multiple integrated circuit (IC) dies per package, at least in part, to help facilitate current handling requirements of the device. One or more of these IC dies can generate junction temperatures in excess of 200 degrees Celsius under normal operation. Consequently, it is critical that a package to which the IC dies are attached has sufficient electrical and heat transfer characteristics so as to allow the packaged semiconductor device to efficiently dissipate this heat.
Most power semiconductor devices employ a ceramic IC package. Ceramic IC packages offer excellent thermal transfer properties. However, ceramic packages are expensive, and in a mass production environment, the ceramic package becomes a primary manufacturing cost of the packaged semiconductor device. While plastic packages are significantly less costly, the plastic package cannot withstand the high temperatures (e.g., about 400 degrees Celsius) generally required for eutectic die attach or soldering, which are typical processes used to secure the die to the IC package. Consequently, alternative methodologies, such as, for example, low-temperature solder or thermal epoxy, are often used to attach the die to the plastic package. These alternative attachment means, however, can significantly reduce the thermal transfer and/or electrical properties of the device and are thus undesirable.
U.S. Pat. No. 6,511,866 to Bregante et al. describes a known methodology that enables eutectic die attach to be used in conjunction with a plastic package. In accordance with this methodology, the plastic package is formed in three separate parts, namely, a base, a sidewall frame and a lid, that are subsequently assembled. First, the plastic sidewall frame of the package is formed by injection molding plastic material over a leadframe. Next, the IC die is attached, using a process such as eutectic bonding, directly to the base of the package. The assembled base is then attached to the bottom of the sidewall frame with an epoxy coating. Finally, the package lid is sealed to the top of the sidewall frame after the die is wire bonded to the leadframe. Although this process may be less expensive than using a ceramic package, a customized plastic package is required, which is still more costly compared to using a standard plastic package. Additionally, because the custom plastic package must be manufactured in three separate parts (i.e., sidewall frame, base and lid), additional steps are required to assemble the package, thus resulting in a lower throughput rate compared to standard plastic IC packaging.
There exists a need, therefore, for an improved semiconductor packaging technique for attaching one or more IC dies in a semiconductor device, that does not suffer from one or more of the problems exhibited by conventional IC packaging methodologies.